January in Isahaya averages a daily high of 10.5°C. Expect roughly 9.8 wet days totalling 64.6mm. Demanding conditions — pack for it and plan indoor options.
Across the year, the best time to visit Isahaya is April–May.
Based on NAGASAKI, JA (20.5km), 1995–2024. 22 years of January data.